1. Field of the Disclosure
The present disclosure relates to a semiconductor light emitting device, and more particularly, to a semiconductor light emitting device having a protrusion and recess structure that is disposed at an interface between a lower clad layer and a side electrode to improve the light extraction efficiency and is formed using a simple manufacturing process and a method of manufacturing the same.
2. Description of the Related Art
A conventional light emitting diode (LED) produces a signal in the form of infrared rays, visible rays, or light from electrical energy using characteristics of a compound semiconductor. A light emitting diode can be electroluminescent (EL) diodes or light emitting diodes using Group III-V compound semiconductor, which are in practical use.
A Group III nitride-based compound semiconductor is a direct transition type semiconductor, and can be used to achieve a more stable operation at a high temperature than other devices using different semiconductors. Therefore, Group III nitride-based compound semiconductors are widely used in light emitting devices such as LEDs and laser diodes (LDs). In general, such Group III nitride-based compound semiconductors are formed on sapphire (Al2O3) substrates. In order to improve light extraction efficiency, research has been conducted on LEDs with various structures, especially on a protrusion and recess structure disposed in light extraction regions of a light emitting device.
At an interface of material layers having different refractive indexes, the transmission of light is dependent on the refractive indexes of the material layers. In the case of a flat interface, when the light is incident from a semiconductor layer with a high refractive index (n=2.5) to an air layer with a low refractive index (n=1), the light is transmitted when the angle of incidence is below a predetermined angle (θ). When the angle of incidence is greater than a predetermined angle, the light is totally reflected at the flat interface, progressed in a lateral direction, and is finally trapped in the LED. Thus, the light extraction efficiency is greatly decreased. The use of a protrusion and recess structure at an interface has been proposed to address this problem.
FIGS. 1 and 2 are cross-sectional views of conventional semiconductor light emitting devices having the protrusion and recess structure.
The semiconductor light emitting device illustrated in FIG. 1 has a PSS (patterned sapphire substrate) structure. Referring to FIG. 1, a GaN buffer layer 11 and a GaN layer 12 are sequentially formed on the sapphire substrate 10. An n-GaN clad layer 13 is formed on the GaN layer 12 and an active layer 14 having a MQW (multi quantum well) structure, a p-GaN clad layer 15 and first and second p-electrode layers 16 and 17 are sequentially formed on the upper surface of one portion of the n-GaN clad layer 13. The first and second p-electrode layers 16 and 17 are respectively a mesh-type p-electrode 16 and a p-electrode pad 17. An n-electrode layer 18 is formed on the upper surface of the other portion of the n-GaN clad layer 13.
Here, the protrusion and recess structure is formed on the sapphire substrate 10. The GaN buffer layer 11 conforms to the structure of the sapphire substrate 10 and the GaN layer 12 has a lower surface that corresponds to the protrusion and recess structure of the GaN buffer layer 11, and a flat upper surface. The light emitting device having the protrusion and recess structure has an advantage in that the light generated from the active layer 14 can be scattered toward the sapphire substrate 10 rather than being trapped. However, a process of forming the protrusion and recess structure on the sapphire substrate 10 is complicated and has a low yield.
In the semiconductor light emitting device of FIG. 2, an n-GaN clad layer 21 is formed on a sapphire substrate 20 and an active layer 22, a p-GaN clad layer 23, a p-type transparent electrode 24 and a p-electrode pad 25 are formed on the upper surface of one portion of the n-GaN clad layer 21. An n-electrode layer 26 is formed on the other portion of the n-GaN clad layer 21. Here, the protrusion and recess structure exists on the surface of the p-GaN clad layer 23. In this structure, the light emitting device has an advantage in that the light generated from the active layer 22 can be scattered toward the p-type transparent electrode 24 rather than being trapped. However, since the thickness of the p-GaN clad layer 23 where the protrusion and recess structure is formed is approximately 0.2 μm, the efficiency of scattering is relatively low. In addition, on the surface of the p-GaN clad layer 23 where the protrusion and recess structure is locally formed, ohmic contact resistance is high, and thus, an operating voltage of the light emitting device is high.